Oh! We have this thing in TV Tropes! We call it a Straw Hypocrite! Indeed, it's a hypothesis always worth assuming, but I don't see how much use it can have except in hindsight, I mean how would one go about predicting someone else's genuine emotional state? It's much easier to predict the emotional state they will allow themselves to show, than it is to try to divine what's going in in that brain of theirs! Not to mention, they probably aren't even actually very clear on what they feel or what they think, at all. In extreme cases, they may have less predictive ability on the topic of their inner workings than an external observer! Not to mention the remarkably ironic occasions where people believe they are "faking" feelings that they actually have and are in denial of!